Well of course I recommend Naruto since it's freaking amazing (and shit just got real recently).
Anything by Hwang Mi Ri and Han Yu Rang is totally worth it. I know they are manhwa and others may not be accustomed to it. I learned a lot about Korean culture through it and they like to reference a lot of real life people which is cool

Yotsuba&!
Lovely Complex
Kitchen Princess
Happy Cafe
X-Day
I Am Here!
Aqua
Be With You
Bunny Drop
HS Debut
Happy Happy Clover (Yes, it may be meant for 9 year olds but do not let that stop you. Read it.)